Valves such as butterfly valves are used to control the flow of fluids, e.g., liquids and gases, in a wide variety of industrial applications such as chemical, power, paper, air conditioning, petroleum and refining industries. Moreover, they are designed to handle clean, viscous and corrosive liquids; clean and corrosive gases; and steam. They are also designed for use in high temperature applications. These valves typically comprise a valve body having a central aperture, and a valve disc mounted within the aperture which can be rotated about an axis to shut off the aperture and halt the flow of fluid therethrough. In further refinements, the valves additionally comprise a sealing gasket or member to make the seal more fluid-tight and leak-proof. In certain applications, flexible rubber or plastic gaskets have been used. Under more extreme conditions, thin metal sealing members have been used to tighten the seal.
Nevertheless, particularly under high pressure and high temperature, leakage continues to be a considerable problem for such valves. The valves of the prior art have not provided sufficient sealing to reduce leakage to desirable levels. One failing of the prior art has been its use of seating rings which are not restrained from moving a substantial distance laterally and under compression when the valve disc is shut and pressure is applied to the valve disc. This excessive bending of the metal seating ring leaves the seating ring vulnerable to deformation and failure over repeated cycles of pressurization. Such a seating ring is consequently vulnerable to pressure extremes and is especially apt to leak when fluid flows in an opposite direction. Such an arrangement is shown in FIG. 1, which itself comprises a figure from U.S. Pat. No. 4,796,857 to Hayes et al., issued Jan. 10, 1989, incorporated herein by reference (numbers are retained from the original figure, with the addition of a prefix of "1" for clarity). As shown therein, the sealing end 120 of the seating ring is located a substantial distance from any support structure. Accordingly, its seating ring is free to flex to a large degree in both directions laterally, and to be compressed to a great degree. This structure permits substantial disc and seat alignment tolerances, but as discussed above, it does not provide an acceptable seal, particularly under extreme operating conditions.
The present invention discloses a unique seal mechanism which provides improved leak resistance, even under extreme conditions of temperature, pressure, and the like. The sealing member, or seating ring, of the present invention, has an inner surface which is permitted to flex and compress only to a certain degree, a degree based preferably on the movement of the valve door itself under maximum rated pressure load. The seating ring also has a bent or ridged construction which allows a spring-type loading of the seal. This is an aid to sealing, particularly at lower pressures.
Another advantage of the present invention is the location of this sealing surface more centrally on the edge of the valve disc. Other sealing mechanisms have been disposed substantially toward one face or the other of the valve disc. Such a location makes the seal far more vulnerable to slippage, displacement and leakage. The seal of the present invention is located substantially equidistant from the two faces of the valve disc. This ensures maximum protection, and in conjunction with the enhanced deformation resistance of the present invention, provides a seal which is much more impervious to leakage, even under extreme conditions.
Another problem which has not been resolved by the prior art is the integrity of the seal when pressure is applied in a direction opposite that of the intended flow of the fluid. The sealing mechanisms of the prior art do not provide adequate means to resist pressure in this opposite direction, and are particularly vulnerable to leakage when fluid generates pressure in this direction. Nonetheless, under operating conditions, pressure is often generated in this direction due to vacuum creation, process shut-off, system maintenance, etc. Leakage in the reverse direction is particularly undesirable because of the risk of contamination and fouling by downstream reaction products which may be contained in such leakage.
In addition, the seating ring retainer design disclosed herein can be modified directly to change face to face joinder dimensions. Such a change is required when the valve is used to connect to a variety of pipes of differing diameters, for instance, or when federal or industry safety or utility standards change. This modified seating ring retainer is much less costly and provides more operational flexibility than the prior art, which uses separate, intermediate bodies to change face to face dimensions.
Another limitation of the prior art is the required maintenance of torque forces on the valve disc when the disc is closed to maintain even a marginal seal. The discs typically used in butterfly valves are double-offset, i.e., they sit on shafts which are offset in two spatial directions from the center of the aperture of the valve. Thus, the shaft is disposed, for example, out of the plane of the disc and closer to one side of the disc than to the other. This arrangement theoretically provides some improvement in the seal generated. In use, however, these seals are prone to leaks, and when fluid is forced against the valve disc, torque must be maintained on the disc to keep it shut. This torque is required because the disc is accepting greater force on one side of the shaft than the other, due to the fact that more disc surface area lies on one side of the shaft than the other. This makes a seal difficult to maintain, increases the energy requirements of the seal, and also makes opening and closing the disc more difficult, which can constitute a safety hazard under operating conditions. In addition, the useful life of such a seal is limited by the repeated application of torque to the disc required to make the valve seal.
The present invention resolves this problem by using a single-offset valve disc mount, together with the sealing mechanism disclosed. Thus, the valve disc rotates on a shaft which is offset from the centerpoint of the valve body aperture in one direction only. The shaft is disposed, for example, out of the plane of, but equidistant from, the sides of the valve disc. Thus, the surface area on one side of the shaft is substantially equal to the area on the other side, so the forces and torques created by fluid pressure on each side are the same. This greatly reduces or eliminates the torque which must be maintained on the disc during use to keep it closed, and contributes to the integrity and durability of the seal. The present invention also positions the shaft as close as possible to the seating ring. This further minimizes the amount of torque required to operate the valve.